1. Field of the Invention
The present invention relates to an ink jet printing method and apparatus which uses a print head having an array of ink nozzles formed therein, color inks containing colorants and a liquid for improving a print performance (hereinafter referred to as a print performance improving ink) and prints an image on a print medium. The present invention is applicable to all apparatus using print media including paper, cloth, leather, non-woven fabric, OHP sheets and even metals. Examples of applicable apparatus include office equipment such as printers, copying machines and facsimiles and industrial production equipment.
2. Description of the Related Art
As the spread of copying machines, information processing devices such as word processors and computers, and communication devices, ink jet printing apparatus as output devices for these equipment to record images have come into increasingly widespread use.
In an ink jet printing apparatus described above, a print head has a plurality of ink nozzles arrayed therein and also a plurality of ink ejection ports and ink passages integrally formed therein to improve a printing speed. In recent years, two or more print heads are used to deal with color printing.
The ink jet printing system ejects droplets of ink or print liquid onto a print medium such as paper to form ink dots on the medium. Because it is of non-contact type, its noise level is low. An increased density of nozzles can enhance the resolution and printing speed, and high quality images can be produced with low cost without requiring special processing such as development and fixing even on such print mediums as plain paper. Because of these advantages, the ink jet printing apparatus is finding a widening range of applications.
An on-demand type ink jet printing apparatus in particular can easily cope with color printing and a printing apparatus body itself can be reduced in size and simplified. Therefore, the on-demand type ink jet printing apparatus is expected to capture a wide range of demands in the future. As the color printing becomes more widespread, there are increasing demands for a higher image quality and a faster printing speed.
In such an ink jet printing system, a technique has been proposed which uses a print performance improving ink capable of improving the condition of color dots on a print medium to enhance an image quality. The print performance improving ink is a colorless or light-colored liquid containing a compound that makes colorants in color inks insoluble. When mixed and/or reacted with color inks on a print medium, the print performance improving ink improves water resistance and weatherability of color dots to produce a highly reliable image quality and at the same time reduces feathering or bleeding between different colors to provide a high quality with high print density.
The conventional ink jet printing apparatus, however, has the following problems even when the print performance improving ink is used.
Where a print head with a plurality of ink nozzles arrayed therein is used, if one or more nozzles are clogged or cannot be driven for some reason, ink cannot be ejected from these nozzles, failing to print dots that need to be printed on the print medium. This results in blank lines being formed on an image extending in a main scan direction, significantly degrading the image quality.
Further, when the print head has faulty nozzles whose ejection conditions greatly differ from those of normal nozzles, a blank line or some form of line due to uneven densities is generated on an image, also degrading the image quality substantially.
Such lines become conspicuous when a multipass printing is not performed or when the number of passes during the multipass printing is small.
To deal with this problem, in the event that there are non-ejecting nozzles or faulty nozzles, it has been a common practice to use a nozzle cleaning mechanism to recover the ejection performance of the non-ejecting or faulty nozzles. When a multipass printing is performed in which one complete printed line is produced by a plurality of passes, a conventional practice has been to replace the non-ejecting or faulty nozzles with complementary nozzles.
The multipass printing system, however, has a drawback that because the paper is fed by {fraction (1/n)} the nozzles used and data which is complementarily culled to {fraction (1/n)} is printed n times during the main scan to print one raster line with a plurality (n) of nozzles, the printing time takes that much longer. The cleaning for recovering the printing performance has a drawback of taking time and causing a cost increase due to consumption of ink. Simply replacing a print head having non-ejecting or faulty nozzles is not desirable in terms of ecology. 
What is required of a future ink jet printing apparatus is to realize a faster printing speed and a reduced cost while at the same time enhancing an image quality.
The present invention has been accomplished in light of the problems described above and it is an object in solving these problems to provide an ink jet printing method and apparatus which, even when there are abnormal (non-ejecting or faulty) nozzles, can print an image with simple processing that has smooth gradations without any image quality degradations including blank lines.
According to one aspect of the present invention to achieve the above objective, the ink jet printing method comprises the steps of: using a color ink print head and a print performance improving ink print head, the color ink print head having a plurality of ink ejection ports arrayed therein, the print performance improving ink print head having a plurality of ink ejection ports arrayed therein; and ejecting a color ink from the color ink print head and a print performance improving ink from the print performance improving ink print head onto a print medium to form an image on the print medium according to input image data; wherein, in forming an image on the print medium, the print performance improving ink is not applied to a dot position corresponding to an abnormal ink ejection port among the plurality of ink ejection ports in the color ink print head which is determined to have a deteriorated ejection state, and to a vicinity of the dot position corresponding to the abnormal ink ejection port.
For example, the print performance improving ink is not applied to a print line corresponding to an abnormal ink ejection port and to at least one line each immediately before and after the print line.
According to another aspect of the invention, the ink jet printing apparatus comprises: a color ink print head having a plurality of ink ejection ports arrayed therein to eject a color ink; a print performance improving ink print head having a plurality of ink ejection ports arrayed therein to eject a print performance improving ink; a means for identifying from among the plurality of ink ejection ports in the color ink print head an abnormal ink ejection port determined to have a deteriorated ejection state; and a control means for not applying the print performance improving ink to a dot position corresponding to the identified abnormal ink ejection port and to a vicinity of the dot position corresponding to the abnormal ink ejection port; wherein the color ink and the print performance improving ink are ejected from these print heads onto a print medium to form an image on the print medium according to input image data.
Because this invention does not apply the print performance improving ink to dot positions corresponding to failed and faulty nozzles and to a vicinity of these dot positions, it is possible to greatly reduce unwanted blank lines in the printed image with simple processing even when some of the nozzles in the color ink head fail or become faulty. Hence, a high quality image can be formed. Further, the ink head with a failed nozzle, or a non-ejecting nozzle, can be used for a long period of time without having to be replaced, which is desirable in terms of ecology.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.